Air circuit breaker

ABSTRACT

An air circuit breaker for interrupting short-circuit currents and which interrupts short-circuit currents up to a predetermined value with a time delay and, at currents exceeding the predetermined value open the associated electric circuit without any time delay.

United States Patent [1 1 [111 3,873,950 Guschin 1 Mar. 25, 1975 AIRCIRCUIT BREAKER 3,593,234 7/1971 Chabonneau 335/176 [7 In entor:vladislav Yakovlevich Guschin, 3,777,293 12/1973 TLlZUkl 335/176Moskovsky prospekt 96, kv. 23,

Kharkov Primary Examiner-G. Harris [22] Filed: May 30, 1973 [211 App].N0.: 365,102

[57] ABSTRACT [52] U.S. Cl. 335/42, 335/176 An air circuit breaker finterrupting shormircuit [51] Int. Cl. HOlh 77/06 Currents and whichinterrupts h t i it Currents up [58] Field of Search 335/24, 42, 175,176 to a predetermined v l with a time delay and, at currents exceedingthe predetermined value open the 1 References Clted associated electriccircuit without any time delay.

UNITED STATES PATENTS 3,525,959 8/1970 Eusworth et a1 335/24 X 4 Claims,2 Drawing Figures Z/ Ij' PATENTEU 3 3,873,950

snmauFz 1 AIR CIRCUIT BREAKER be disconnected and that all othercircuits remain connected to supply. To this end, the air circuitbreaker nearest to the source of supply is furnished with a deviceproducing a time delay longer than the operating time of any of thecircuit breakers located between it and the load.

When the circuit breaker nearest the load is capable of interrupting theshort-circuit current within a period of time shorter than a part of thetime delay, usually ranging from 70 to 90 per cent of the circuitbreaker nearest to the source of supply, the latter breaker will notopen at all.

If the circuit breaker nearest the load is unable to interrupt theshort-circuit current in the course of the indicated period of time, thefaulty circuit will be opened by the circuit breaker nearest to thesource of supply on expiration of the time delay of the latter breaker.Such a method of circuit protection is known as selective protection,and air circuit breakers operating with a current-independent time delayare referred to as selective circuit breakers.

It is apparent from the above-said that one of the main requirements tobe met by selective circuit breakers is their capability to withstandthe injurious effect of short-circuit current throughout a considerabletime delay.

Air circuit breakers used for operation under selective duty conditionsare designed to carry a considerably heavier rated current than isrequired according to normal conditions of operation of the electriccircuit in which the given circuit breaker is included.

Such air circuit breakers possess a high electrodynamic and thermalstability due to the high contact pressure and large cross-sectionalarea of their currentcarrying parts.

This high contact pressure calls for a large size of the breakermechanism, and current-carrying parts oflarge cross-sectional areaincrease both the weight and the cost of such air circuit breakers.These disadvantages set limits on the use of air circuit breakers ofhigh current ratings as selective breakers.

Also known in the art are small-size selective circuit breakers whereina high electrodynamic stability is attained by use of an electrodynamicdevice for balancing the forces of repulsion arising between the breakercontacts during the passage of short-circuit currents rather thanresorting to a high contact pressure.

An air circuit breaker intended for operation under selective dutyconditions is already known. This air circuit breaker comprises a manualoperating mechanism, a system of contacts, and electrodynamic device forbalancing the electrodynamic forces of repulsion acting on the contacts,emergency tripping devices and a freetrip mechanism. The device used forbalancing the electrodynamic forces of repulsion acting on the contactsduring the passage of a short-circuit current through the conductors ofthe device gives rise to electrodynamic forces that act upon one of thecircuit breaker contacts and balance the force of contact repulsion.These additional balancing forces are transmitted through links of thefree-trip mechanism to the system of engaged elements of the free-tripmechanism.

The size of the overcurrent tripping device is reduced by using afree-trip mechanism requiring a small actuating force for its operation.For this purpose, one or more lever-type intermediate elements thatallow reducing the force transmitted to the element actuated by theovercurrent tripping device are introduced between the main trippingelement and the element acted upon by the overcurrent tripping device.

A disadvantage of air circuit breakers of this type is that they triponly after full expiration of the pre-set time delay on occurence of ashort circuit located directly after the circuit breaker. Therefore, thecrosssectional area of the current-carrying parts of the circuit sectioncontiguous to the air circuit breaker has to be selected based on thethermal and electrodynamic effect of the longitudinal short-circuitcurrent over the entire duration of the circuit breaker time delay.

Moreover, the mechanical effect of the short-circuit current upon thecurrent-carrying parts of the air circuit breaker itself and themechanical forces transmitted by the elements of the operating mechanismalso act over the full time delay of the circuit breaker.

As a result, the current-carrying parts and operating mechanism elementsof the air circuit breaker are designed to withstand the continuousthermal and mechanical action of the maximum short-circuit currentliable to flow in the protected electric circuit, this circumstanceleading to a considerable increase in the cost and size of the aircircuit breaker as compared with circuit breakers that clear the shortcircuit without any time delay and, consequently, hindering standard'ization of the circuit breaker sizes.

It is a general object of the present invention to eliminate theabove-mentioned disadvantages of known air circuit breakers.

A further object of the herein described invention is to provide an aircircuit breaker adapted to open the protected circuit without any timedelay as soon as the short-circuit current reaches a predeterminedvalue.

These and other objects are attained in a novel air circuit breakercomprising a manual operating mechanism, a system of moving contacts, adevice for balancing the electrodynamic forces of repulsion acting uponthe mentioned contacts, emergency tripping devices and a free-tripmechanism provided with a latch and a tripping rod, so that the latch onbeing engaged with the tripping rod holds the free-trip mechanism inposition corresponding to the closed position of the circuit breakercontacts, characterized according to the present invention by that thelatch of the free-trip mechanism is mounted on a shaft within a supportand is capable of travelling together with the shaft in respect to saidsupport in the direction of disengagement of the latch with the trippingrod, said latch being provided with a device for keeping the latchengaged with the tripping rod.

The device for keeping the latch engaged with the tripping rod may bein'the form of a spring mounted so that it acts upon the latch in adirection opposite to the travel of the latch on its disengaging withthe tripping rod.

The device for keeping the mentioned latch engaged with the tripping rodis preferablyfurnished with an adjusting device made, for example, inthe form of a screw attached to one end of a tensioning spring.

The adjusting device allows the pull of the spring that keeps the latchengaged with the tripping rod to be varied, thus providing for accuratesetting of the circuit breaker operating current.

In order to disengage the latch and tripping rod with minimumdisplacement of the latch in the direction of disengagement and,consequently, to shorten the time of disengagement, the air circuitbreaker is preferably furnished with an arrester that prevents thetripping rod from rotating in the direction of increase of itsengagement with the latch due to the effedt of frictional'forces actingat the point of engagement.

The present invention will further be described by drawings, wherein:

FIG. 1 is a general schematic representation of the aircircuit breakerin accordance with the present invention; and

FIG. 2 is an enlarged view of assembly A of the air circuit breaker inaccordance with the present invention.

The automatic air circuit breaker of the invention comprises a system ofcontacts including a moving conductor 1, a carrying contact 2, a contact3 directly connected with a device 4 that serves for balancing theelectrodynamic forces of repulsion. The device 4 comprises a coil builtup of two conductors made so that a conductor 5 of the coil is fixed tothe circuit'breaker, whereas a conductor 6 is free to move a couplingshaft 7 of both conductors and carries the contact 3 that establishes anelectrical contact with said contact 2 when the air circuit'breakercloses. A spring 8 produces the required contact pressure at closure ofthe air circuit breaker.

The moving conductor 1 and the coil moving conductor 6 have extendedends that perform the function of arcing contacts. The moving condutor lis hinged with a system of collapsible links 9 and 10 and a trippinglever ll.

The manual operating mechanism of the air circuit breaker comprises anoperating handle 12 and a spring 13, one end of which is attached to thehandle 12 while the other end is coupled with the common joint (notshown in the drawing) of links 9 and 10. When the air circuit breaker isin closed position, the lever 11 is engaged with a latch 14.

The latch 14 is hinged to a rest 15 and with the air circuit breaker inclosed position is engaged with a tripping rod 16. A hole 17 ofthe rest15 holding a shaft 18 of the latch 14 is elongated in the direction ofdisplacement of the shaft 18 and the latch 14 corresponding to decreaseof engagement of the latch 14 with the tripping rod 16.

When the air circuit breaker is in closed position, a spring 19 keepsthe shaft 18 of the latch 14 in the extreme position within the rest 15at which the latch 14 is engaged with the tripping rod' 16. The otherenriZ-bl' the spring 19 is attached to an adjusting screw 20 used forvarying the pull of the spring 19. The tripping rod 16 is hinged with asupport 21 wherein an arrester 22 is provided to prevent the trippingrod 16 from rotating in the direction of increase of its engagement withthe latch 14.

An overcurrent tripping device 23 meant for emergency tripping of theair circuit breaker is fitted with a moving rod 24 that serves forrotating the tripping rod 16 in the direction of its disengagement withthe latch 14. The moving conductor 1 is connected electrically with aterminal 25 of the air circuit breaker by means of a flexible lead 26.

The air circuit breaker operatesin the following manner.

In the event of a shortcircuit thathas to be cleared without any timedelay, the short-circuit current passing through the closed contacts 2and 3 produces electrodynamicforces of repulsion that tend toseparatethe contacts and are caused by narrowing of the current elementary linesat the point of contact. At a maximum value of the short-circuitcurrent, these forces are much greater than the pull exerted by thespring 8.

Passage of the same current through the conductors of the device 4 givesrise to electrodynamic forces between the fixed conductor 5 and themoving conductor 6. As this takes. place, the upper part of conductor 5and the conductor 6 in which the current flows in one and the samedirection experience a force of attraction, whereas the lower part ofconductor 5 and the conductor 6 in which the current flows in oppositedirection experience a force of repulsion. The net force acting betweenthe conductor 5 and the conductor 6 of device 4 prevents separation ofthe contacts 2 and 3,'whatever the magnitude of the short-circuitcurrent. The magnitude of the force varies directly with the value ofthe short-circuit current. The force is applied to the moving conductor1 via the contacts 2 and 3. In consequence, the moving conductor 1 actsthrough the links 9 and 10 upon the lever 11,.the latch 14 and thetripping rod 16 with which it is engaged.

With the short-circuit current at predetermined value, the force actingupon the latch 14 exceeds the pull exerted by the spring 19 and thelatch 14 moves together with the shaft 18 coupling it with the rest 15within the elongated hole 17 of rest 15. As a result, the latch 14 andthe tripping rod 16 become disengaged.

After the latch 14 has been released, it disengages the lever 11. Theaction of spring 13 upon the lever 11 on its disengagement from thelatch 14 causes the lever to rotate counterclockwise about its shaft asfar as it will go. As a result, the shaft coupling the link 9 and thelever 11 will be to the left'of the axis of spring 13, the links 9 and10 turn in respect to each other, and the moving conductor 1 coupledwith the link 10 moves upwards, thus opening the contacts 2 and 3 of theair circuit breaker.

The air circuit breaker should preferably be provided with an adjustingdevice for setting the required value of the circuit breaker operatingcurrent interrupted without any time delay.

FIG. 2 illustrates the embodiment of the adjusting device.

One end of the spring 19 is attached to the adjusting screw 20, and theother end is held by the shaft 18 of the latch 14. A nut 27 is fitted onthe screw 20 so as to keep the latter in fixed position. The pull ofspring 19 is varied by moving the nut 27 along the screw 20.

The latch 14 during its movement within the hole 17 of the rest 15 mayrotate the tripping rod 16 counterclockwise due to the action offrictional forces present at the point of engagement of the latch 14 andthe tripping rod 16. This is an undesirable effect as it preventsdisengagement of the latch 14 and the tripping rod 16.

To avoid this effect, the air circuit breaker should preferably beprovided with the arrester 22 that limits the rotation of the trippingrod16 in the direction at which the magnitude of its engagement with thelatch 14 does not diminish.

In accordance with the present invention, when the automatic air circuitbreaker of the present embodi' ment interrrupts short-circuit currentsand it is desired to have a time delay, the circuit breaker operates asan ordinary selective circuit breaker.

In this case, the force developed by the device 4 is insufficient toovercome the pull of spring 19. The latch 14 and its shaft 18 remain inthe lower extreme position within the elongated hole 18 of rest 15throughout the entire period of passage of the short-circuit current.

On expiration of the time delay, a rod 24 of the overcurrent trippingdevice 23 acts upon the tripping rod 16 and turns it through an anglerequired for disengagement from the latch 14. Further the air circuitbreaker opens in the same way as described above.

The herein described air circuit breaker operates selectively up to acertain predetermined value of the short-circuit current and, at passageof short-circuit currents exceeding the predetermined value, the aircircuit breaker opens the electric circuit without any time delay andcurrent limitation.

Use of the proposed air circuit breaker allows reducing the size of theelectric power distribution circuits selected according to the maximumvalue of the shortcircuit current and in conjunction withcurrent-limiting circuit breakers improve the protection of the powersupply transformers of switchgear installations.

What we claim is:

1. An air circuit breaker comprising: a manual operating mechanism; asystem of moving contacts having open and closed positions; first meansfor balancing the electrodynamic forces of repulsion acting upon saidmoving contacts; emergency tripping devices; a freetrip mechanismadapted to effect control of said contacts;

said free-trip mechanism including a latch for action on said firstmeans and a tripping rod;

said latch on being engaged with said tripping rod holding saidfree-trip mechanism in position corresponding to the closed position ofsaid moving contacts, a support, a shaft displacably supported by saidsupport, said latch being mounted on said shaft and being capable oftravelling together with said shaft in a direction effectingdisengagement of said latch from the tripping rod; second meansresiliently tending to keep said latch engaged with said tripping rod;said second means including an adjusting means;

said adjusting means providing for adjustment of the magnitude of theforce keeping said latch engaged with the tripping rod, thus allowingselection of a value of circuit breaker operating current.

2. An air circuit breaker according to claim 1, wherein said secondmeans is in the form of a spring mounted so that said spring acts uponsaid latch in a direction opposite to the movement of said latch on itsdisengaging from said tripping rod.

3. An air circuit breaker according to claim 2,.

wherein said adjusting means comprises a screw attached to said springand adjustable for providing for various degree of pull of said spring.

4. An air circuit breaker according to claim 1 wherein said tripping rodis rotatable, including an arrester that prevents said tripping rod fromrotating under the action of the frictional forces present at the pointof engagement with said latch in the direction of increase of itsengagement with said latch.

l= l l= i

1. An air circuit breaker comprising: a manual operating mechanism; asystem of moving contacts having open and closed positions; first meansfor balancing the electrodynamic forces of repulsion acting upon saidmoving contacts; emergency tripping devices; a free-trip mechanismadapted to effect control of said contacts; said free-trip mechanismincluding a latch for action on said first means and a tripping rod;said latch on being engaged with said tripping rod holding saidfree-trip mechanism in position corresponding to the closed position ofsaid moving contacts, a support, a shaft displacably supported by saidsupport, said latch being mounted on said shaft and being capable oftravelling together with said shaft in a direction effectingdisengagement of said latch from the tripping rod; second meansresiliently tending to keep said latch engaged with said tripping rod;said second means including an adjusting means; said adjusting meansproviding for adjustment of the magnitude of the force keeping saidlatch engaged with the tripping rod, thus allowing selection of a valueof circuit breaker operating current.
 2. An air circuit breakeraccording to claim 1, wherein said second means is in the form of aspring mounted so that said spring acts upon said latch in a directionopposite to the movement of said latch on its disengaging from saidtripping rod.
 3. An air circuit breaker according to claim 2, whereinsaid adjusting means comprises a screw attached to said spring andadjustable for providing for various degree of pull of said spring. 4.An air circuit breaker according to claim 1 wherein said tripping rod isrotatable, including an arrester that prevents said tripping rod fromrotating under the action of the frictional forces present at the pointof engagement with said latch in the direction of increase of itsengagement with said latch.